Hand-held trace vapor/particle sampling system

ABSTRACT

A sampling system that contains filter components for collecting and concentrating vapor and particles in high-volume flows. The sample is then vaporized and delivered to a detector at a low-volume flow. The invention also has a sampling probe that contains an air-jet to help dislodge particles from surfaces and a heating lamp to help vaporize compounds on surfaces or objects. The sampling system is especially useful for screening for explosives and other illicit chemicals and toxins on people, baggage, cargo, and other objects.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of claiming priority toU.S. application Ser. No. 11/202,455, filed Aug. 11, 2005 now U.S. Pat.No. 7,299,710.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of detection apparatus usedto screen for the presence of explosives and other chemical entities.

2. Background Information

An effective screening system for threat compounds such as explosives aswell as chemical and biological weapons must be able to collect,concentrate, and analyze trace samples quickly and accurately. Manydetection technologies (e.g., mass spectrometry, ion mobilityspectrometry, optical spectroscopy, etc.) have been developed over theyears and trace detectors now exist that can detect a wide range ofexplosives and chemical weapons, and to a lesser extent biologicalweapons. Much less attention has been given to collecting and deliveringsample to the detectors, yet this is arguably the most challenging partof a screening system since it must adapt to a wide range ofapplications and screening scenarios. Furthermore, whereas thespecificity of a detector is the key to minimizing false positive rates,the collector/concentrator is of vital importance for maximizingdetection rates, since if a trace sample is not delivered to thedetector, it will result in a non-detect event.

An effective sampling system must have the following operationalcharacteristics: (1) access the volume containing the contamination, (2)dislodge the contamination, particularly for particles that can sticktightly to materials, (3) concentrate collected vapor and particlematerial, (4) deliver the material to a trace detector in a step thatinvolves vaporization, and (5) minimize cycle time and carryovereffects.

An effective collector/concentrator sampling system for explosives andother threats must be able to collect vapor and particles, and ifdelivering to a trace detector, convert the particles to vapor. Severalvapor and particle sampling systems have been developed in the past,however, they are either optimized for one or the other phase, or arenot suitable for trace detectors.

U.S. Pat. No. 6,087,183 issued to Zaromb discloses a method to collectvapor and particles on a liquid film. However, a liquid concentrate isnot the preferred medium for a trace detector, which is designed toanalyze vaporized sample. U.S. Pat. No. 5,914,454 issued to Imbaro etal. discloses a spray of charged droplets to collect vapor, liquid, andparticles, but the sample is also concentrated in a liquid. U.S. Pat.No. 5,855,652 issued to Talley discloses a method for collectingparticles and microorganisms into a water sample. U.S. Pat. No.4,092,218 issued to Fine et al. discloses a method for the selectivedetection of explosives vapors, but does not show that it is capable ofcollecting particles.

A series of patents issued to Linker et al. disclose methods to collectexplosives particles for trace detectors that have some capability tocollect vapor as well. U.S. Pat. No. 6,345,545, issued to Linker et al.,discloses a two-stage preconcentrator that uses a metal or otherelectrically conducting screen to capture particles. Some vapors mayalso stick to the screen, however, the surface chosen for particlecollection is not in general optimal for vapor collection. U.S. Pat. No.6,523,393, issued to Linker et al., discloses a hand-portable embodimentof the metal screen particle concentrator that makes use of a removablescreen that is manually placed first in the high volume flow region andsecond in the detector region.

The above patents disclose means for sample concentration. Anotherimportant component to an overall screening system is a sampling probefor collecting vapor and particles, particularly from hard-to-removelocations and surfaces. U.S. Pat. Nos. 6,334,365 and 5,915,268 issued toLinker et al., disclose the use of air-jets to help dislodge particlesfrom the clothing of individuals in a portal device for screening peoplefor explosives. U.S. Pat. No. 6,708,572, issued to Jenkins et al., alsodiscloses the use of air-jets to dislodge particles from individuals ina portal device.

Trace detectors are extensively in airports and other venues to screenbaggage for explosives. The method typically used to remove materialfrom surfaces are swipes of cloth. This method is effective atcollecting residue, however, it requires manual operation and thereforemay produce unpredictable results in the collection process. Furthermoreit is not effective at collecting vapors.

BRIEF SUMMARY OF THE INVENTION

A concentrator that collects and transfers a sample. The concentratorincludes a vapor filter and a particle filter. The particle filter isheated to a temperature that also heats the vapor filter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of vapor/particle concentrator;

FIG. 2 is an illustration showing a sampling probe with an air-jetnozzle and heating lamps;

FIG. 3 is an illustration of a sampling system including a samplingprobe and a vapor/particle concentrator coupled to a detector;

FIG. 4 is a timing diagram for the sampling system;

FIG. 5 is an illustration of an alternate embodiment of the samplingsystem;

FIG. 6 is an illustration of a device for coupling a removablevapor/particle filter assembly to a detector;

FIG. 7 is an illustration of a removable vapor/particle filter assembly.

DETAILED DESCRIPTION

Disclosed is a sampling system that contains filter components forcollecting and concentrating vapor and particles in high-volume flows.The sample is then vaporized and delivered to a detector at a low-volumeflow. The invention also has a sampling probe that contains an air-jetto help dislodge particles from surfaces and a heating lamp to helpvaporize compounds on surfaces or objects. The sampling system isespecially useful for screening for explosives and other illicitchemicals and toxins on people, baggage, cargo, and other objects.

Referring to the drawings more particularly by reference numbers, FIG. 1shows an embodiment of a collection system 10. The system 10 includesporous filters 12 and 14 for the collection of vapors and particles,respectively. The filters 12 and 14 are coupled to a housing 15.Particle and vapor sample in region 16 is pulled through the filters 12and 14 by a pump 18 in region 20. The particle and vapor in region 16may be enhanced by a device 22 for removing and collecting the samplefrom remote locations. Filters 12 and 14 have reasonably large area andporosity in order to allow a high volume of flow to pass through thefilters. The filter diameters could typically range from ¼ inch toseveral inches in size. It is preferable to have the particle filterfirst so that particles are not trapped on the vapor filter. Some vaporsample may partially stick to the particle filter, however, the vaporfilter is optimized for vapor collection and would collect all or mostof the vapor in the air flow.

After a period of time for collecting vapor and particles, theconcentrator 10 is then switched to a mode to deliver a sample to adetector 24. Valves or shutters 26 a and 26 b may be used to close offand isolate the filters 12 and 14 from regions 16 and 20. The filters 12and 14 are then heated to vaporize the collected vapor and particles.One version of a particle filter is a screen or mesh made of metal orother electrically-conducting material. This type of filter is desirablebecause it can be rapidly heated by passing a current through it. Theheating vaporizes the particles. The current may be provided by thecontroller 30. The vapor filter can be constructed from anon-electrically conducting material such as a polymer or similarmaterial known for having a high adsorption coefficient for vapors. Inorder to remove the vapor, the filter must also be heated. This can beachieved by the heat from the particle filter. The particle filteressentially acts as a “toaster” to heat the vapor filter to remove thevapor.

The system 10 may further contain a low-volume flow source 28 totransfer the vaporized collected sample to the detector 24. The system10 may include a conduit 30 to the detector 24 which is an open tube, aseries of apertures, or other means of fluid communication. The detector24 can detect trace compounds within the sample. By way of example, thedetector 24 may be a mass spectrometer or other detection system. Thevarious elements of the system may be controlled by a controller 40.

FIG. 2 shows an embodiment of a sampling probe 50 to enhance thecollection of vapor and particles from surfaces or remote volumes. Theprobe includes a sampling head 52 that contains an air-jet nozzle 54.The head 52 may also include heating lamps 56. The air-jet nozzle 54 maybe connected to a gas line 58, a shut-off valve 60 and a pump orcompressor 62 that deliver a high-pressure flow of gas or air to thenozzle 54. The air-jet nozzle 54 may deliver gas pulses, or a continuousstream of gas. The air-jet nozzle 54 is used to help dislodge particlesand residue from surfaces and objects such as baggage or people. Somechemicals on these objects may be liquids or have higher volatility thanparticles, such as some explosives and chemical weapons. In these casesit may be advantageous to apply heat to the surface or objects to raisethe vapor pressure of these chemicals. This can be accomplished byturning on the heat lamps 56. By way of example the lamps 56 may becommercially available infrared lamps.

The air-jet nozzle 54 and lamps 56 are operated sufficiently long toremove sample from objects. The vapor and particle in region 64 is thendrawn to a concentrator or other collection means by a pump 66 through acollection line 68. The concentrator may be the system shown in FIG. 1of the drawings.

FIG. 3 shows an embodiment of sampling system 100 consisting of asampling probe 50′ and a concentrator system 10′. Similar to FIG. 2, thesampling probe 50′ includes an air-jet nozzle 54′, heating lamps 56′, apressured gas line 58′ and a valve 60′. The sample is drawn to theconcentrator 10′ through sampling line 68′. The concentrator 10′ in FIG.3 consists of a vapor/particle filter assembly 110, valves 112, 114, and116, pump 118, and a gas flow assembly 120. The pump 118 acts to supplyan over-pressure of air or gas to the air-jet nozzle 54′ and to pull thesample volume through the collection line 68′.

The sampling system 100 first collects sample by turning the pump 118on, opening valves 112 and 114 and closing valve 116. During this periodthe air-jet nozzle 54′ and lamps 56′ operate as described relative toFIG. 2. After a sufficient sample collection time, the pump 118 may bedeactivated, valves 112 and 114 may be closed, and valve 116 may beopened. The vapor/particle filter assembly is then heated in the mannerdescribed relative to FIG. 1 and a gas-flow from source 120 carries thevaporized sample to a detector or other device 124. It is also possibleto operate 10′ without the use of valve 116 if the volume of the linegoing to the detector 124 is relatively low and not open to the outsideenvironment. All other operations would be the same. The operation andtiming of the sampling system 100 is controlled by a controller 130.

FIG. 4 shows a timing diagram for the sampling system 100. The high andlow states in the diagram denote on and off for the respectivecomponents. As described above during the collection period the firstand second valves 112 and 114 are open and the third valve 116 isclosed. During this period the air nozzle 54 and lamps 56 may beoperated. The collection period may range from about 1 second to a fewminutes depending on the speed and sensitivity needed for a particularscreening application. As noted above, following the collection period,valves 112 and 114 may be closed and valve 116 may be opened. The filterassembler is then heated and the concentrated sample thermally desorbsand flows to a detector, reaching a maximum concentration until allsample is desorbed. This step may typically take from about 1 second toabout 1 minute.

It may be necessary to recycle the filter assembly following thedesorption period after the sample has been delivered to the detector.This may be achieved by further heating the filter assembly to drive offremaining sample. For example if an explosives or other targetedchemical is collected in high concentration, it may be necessary torecycle the filter assembly a few times to remove remaining traces inorder to be able to screen again at high sensitivity without having toworry about sample carryover from a previous screen. The recycle periodmay typically last from a few seconds to a few minutes. The recycleperiod also allows the filter assembly to cool down by initiatingeffectively a collection period sequence, but with the air nozzle 54 andlamps 56 in the off state. For fast screening it will be typical for thecollection, desorption, and recycle periods to last only a few secondseach.

It may be convenient to have separate assemblies for the samplecollection phase and for the sample delivery phase. This would be thecase where there is a need for several sampling devices with a singledetector unit or when it is necessary to go to remote locations tocollect sample. FIG. 5 shows an embodiment of a sampler and concentrator150 that consists of a sampling probe 52, a vapor/particle filterassembly 110′, a pump 118′, and other components described relative toFIG. 2. This embodiment enables the sampler and concentrator assembly tobe used away from the detector. It can also be made into a hand-heldunit. One possible application is as a sampler for screening baggage forconcealed explosives. The operation works similarly to that describedfor the sampling system 100 in FIG. 3, except that the device 150 inFIG. 5 does not deliver the concentrated sample to a detector or otherdevice.

FIG. 6 shows an embodiment of a device 160 that would enable delivery ofconcentrated sample from a vapor/particle filter assembly 110′ to adetector 124′. The filter assembly 110′ may be removed from the samplesshown in FIG. 5. The filter assembly 110′ is heated to desorb thecollected vapor and particles in the manner described for concentrator10. The device 160 may include a low volume source 128′ that iscontrolled by controller 130′. Because the embodiment of 160 is notdirectly connected to the sample collection assembly, it is notnecessary to have valves that isolate the filter assembly from the mainflow.

Because the thermal desorption period and subsequent analysis by thedetector typically takes much less time than the collection andrecycling periods, the utilization of the combinedsampler/concentrator/detector system can be improved by using multiplesampler/concentrator assemblies for a particular detector. A system mayinclude several hand-held sampler/concentrator systems 150 that collectsamples from multiple objects and then transfer the filter assembly 110′to the delivery and detector system 160. Because several filterassemblies may stack up waiting for analysis, it is necessary to have asystem to keep track of the samples.

FIG. 7 shows an embodiment of a removable and reusable vapor/particlefilter assembly 200. The assembly 200 may include particle and vaporfilter screens 210. The assembly 200 may also include electricalcontacts 220 a and 220 b to provide connections to the particleelectrically-conducting mesh for passing current to heat the mesh. Toassist in transporting the filter screens 210 to the detector theassembly may include a handle 222. The assembly may include a bar code230 that can be read to keep track of the samples.

When the filter assembly 200 is inserted into the delivery assembly 160,the pick-up flow of gas comes from source 240 and goes in the directionof 242 toward the detector. The bar code can also be used by either thesampler 150 or the delivery assembly 160 to keep count of the number ofsamples the filter assembly has been used for. This is convenientfeature because it can alert operators to the end of the useful life ofthe filter assembly 200 or to a service and maintenance schedule.

For the hand-held sampler configuration 150, power may need to beprovided by battery. By way of example we discuss typical pumpingspeeds, flow rates and concentration factors, as well as consumed power.Table I summarizes the air flow and power characteristics of the samplecollector/concentrator.

TABLE I Concentrator specifications Peak power consumption Collectionflow × time: IR lamps: 50-100 W 24 L/min × 5 s = 2.0 L Pump: 20-40 WDetector flow × time: Sampling line heater: 15 W 0.24 L/min × 5 s =0.020 L Valve: 5 W Concentration factor: 5.0 L/0.0125 L = 100 Cycletime: 20 s (incl. 10 s recovery)

The collection flow must draw the sampling volume over the surface orobject, which we assume for this example to be about 2 L. The volume inthe sampling line 68 (e.g., 3 cm ID×10 cm ˜0.1 L) is insignificantrelative to the sampling volume and can be ignored. A small pump of 24L/min can pull the 2 L sampling volume through the filter assembly 110′in 5-6 sec. Such a pump can be operated with about 10-20 W of power. Foroptimum use of the air-jet nozzle it may be preferable to use a largerpump. A 100 L/min blower pump consumes about 20-40 W of power. Manytypes of heating lamps 56 may be used. High efficiency IR lamps fordevice 150 would consume about 50-100 W when operated. If valve 60 isused and heating elements on the inside of the sampling line 68 areused, then there will be a need for another 20 W of power for a totalpeak power of 90-160 W. This peak power is operated for about 5 sec. persample.

A nickel metal hydride battery, like a computer battery, delivers about40 W hr per pound. A two pound battery would then give 30 min of 160 Wpeak power. At 5 sec. per sample this would give 360 samples. Assumingone sample is collected every minute, then the battery would last 6 hr.The values given above are by way of example only. Other choices ofbatteries and power management may be used to extend or change thisperiod if necessary.

We now consider the concentration factor and potential sensitivity ofthe disclosed sampler embodiments particularly the sampler/concentrator150 and the thermal desorber 160. The vapor and particle that iscollected on the filter assembly 110′ is thermally desorbed as a vapor.A flow rate of 0.12 L/min into the detector corresponds to an enrichmentfactor of 100× (Table I). If the internal volume of the filter assembly110′ and the volume of the inlet to the detector 124′ is about 10 cm³,then the flow needs to be on for 5 sec. to completely deliver thevaporized sample. In terms of total mass of compound collected, 1part-per-billion of a target compound of MW 200 in the 2 L samplingvolume in region 64 corresponds to about 16 ng. If a detector has asensitivity of 16 pg, then a sensitivity at the sampling volume 64 of 1part-per-trillion is possible. This sensitivity may be improved byextending the collection period to times longer than 5 s.

The systems and devices shown and described can be utilized to detectsamples of trace explosives contamination on baggage, cargo, andpersonnel due to concealed explosive devices. Trace contamination isknown to be pervasive throughout the bomb making and bomb packingprocess. This contamination can take the form of vapor for more volatileexplosives (e.g., the class of nitrate esters and nitro toluenes, aswell as taggant compounds) or particles for the more crystalline forms(e.g., the nitramines RDX and HMX).

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive on the broad invention, andthat this invention not be limited to the specific constructions andarrangements shown and described, since various other modifications mayoccur to those ordinarily skilled in the art.

What is claimed is:
 1. A probe for collecting a trace sample from anobject for detection by a detector, comprising: a housing comprising anozzle configured to direct a jet of fluid onto the object and acollection line for collecting the trace sample from the object, whereinat least a portion of said collection line is positioned proximate saidnozzle; wherein the collection line comprises a plurality of valvesconfigured to control a flow of the jet of fluid through said nozzle anda flow of the fluid through said collection line in a predeterminedsequence that facilitates dislodgment and collection of the trace samplefrom the object; and a controller coupled to said plurality of valvesfor controlling said plurality of valves, wherein said plurality ofvalves comprises at least three valves.
 2. The probe of claim 1, whereinthe jet of fluid is one of substantially continuous and pulsed.
 3. Theprobe of claim 1 further comprising at least one heating element coupledto said housing.
 4. The probe of claim 3, wherein said at least oneheating element comprises an infrared lamp.
 5. The probe of claim 1,wherein said plurality of valves comprises a first valve, a secondvalve, and a third valve, wherein the sample collection is facilitatedwhen said first valve is open, said second valve is closed, and saidthird valve is open.
 6. The probe of claim 5, wherein said plurality ofvalves comprises a fourth valve, wherein said fourth valve is open tofacilitate dislodgment of the sample.
 7. A method for collecting a tracesample from an object for detection by a detector, comprising: directinga jet of fluid onto the object through at least one nozzle; collectingthe trace sample from the object through a collection line comprising aplurality of valves, wherein at least a portion of the collecting lineis positioned proximate the nozzle; and controlling a flow of the jet offluid through the at least one nozzle and a flow of the fluid throughthe plurality of collection line valves in a predetermined sequence,thereby facilitating dislodgement and collection of the trace samplefrom the object, wherein said plurality of valves comprises at leastthree valves.
 8. The method of claim 7, wherein the jet of fluid iscontrolled to be one of continuous and pulsed.
 9. The method of claim 7further comprising heating the object.
 10. The method of claim 9,wherein said heating the object comprises energizing at least oneheating element.
 11. The method of claim 10, wherein said energizing atleast one heating element comprises energizing at least one infraredlamp.
 12. The method of claim 7, wherein said controlling the flow ofthe fluid through the plurality of collection line valves in apredetermined sequence comprises opening a first valve, closing a secondvalve, and opening a third valve.